European starlings, Sturnus vulagaris, on wires -- click to enlarge.
It was very windy in Brooklyn yesterday. Birds on wires were all facing in the same direction. On a still day or in sheltered areas, birds sit facing any direction. But when the wind is blowing they turn to face it -- not just on wires but also on beaches, on branches, in fields, at feeders, on fences, and everywhere else. They are streamlined and the wind flows smoothly around them. If they faced the other way, it would ruffle up their feathers and let cold air under, and it might push them off balance. Like airplanes, birds land into the wind. They take off into the wind like airplanes too, and for the same reason -- they get aerodynamic lift. As they sit facing the wind, they are ready to step into the air and fly.